The invention relates to a pulse motor driving system including a memory storing a minimum amount of control data for determining the time series of drive pulses to control the speed of pulse motor in accordance to a number of moving steps. According to the invention, a limited amount of time series control data is used to calculate out the time series code signals for controlling the stepping speed with a pulse motor in accordance to the number of steps needed by the pulse motor to move a given distance.
Generally a pulse motor has to be driven a given distance with comparatively many steps within a limited interval of time. As the result, vibrations are produced in the accelerating and decelerating directions due to the inertia of the motor and the load thereof. In order to reduce such vibrations, groups of data are stored as the time series codes which are each specific to the sections of different numbers of steps to give suitable pulses to the motor all through the driving sections. These groups of data are selectively designated each time the moving steps of the pulse motor are designated, thereby to control the speed of the motor. It is however a drawback of this method to require a very big data storing capacity.
There is a trapezoidal driving method as a way of minimizing the data storing capacity as is disclosed in detail in the copending U.S. patent application Ser. No. 131 357 or in copending West German patent application No. P 30 11 715.8 of the same applicant. Brief explanation of this is as follows; In reference to FIG. 1, in which the lateral axis shows a time ( t seconds), i.e., the accumulation of time intervals between the adjacent pulses and the vertical axis shows a speed of pulses, i.e., a number of pulses PPS per second, the speed of pulses is increased from a point 0 to a point A with a sufficient acceleration in a section of comparatively many steps, so that the pulse motor may mechanically follow the start, and then a high speed is constantly maintained in the section between the points A and B, and then the speed is decreased as the motor comes to stop in the section between the points B and C so that the motor may properly follow the speed. Thus the number of steps is designated by the drive steps which are determined by the size of trapezoid surrounded by lines O A B C. The shape of trapezoid is determined on a condition that a time interval is comparatively short from start to stop of the motor, the motor properly follows the speeds of pulses, and vibrations will not be produced at the speed changing points A, B, C. The data comprising time series codes of pulses are all stored in an electronic memory which are plotted generally with an uneven space therebetween on the lines O A B C, though with an even space therebetween on the line A B in this case.
These data may be used to control a comparatively small number of moving steps of pulse motor. Namely, in response to a designation of moving steps, a number of steps are accorded with the designation of moving steps by way of a space defined by a line OD on the line OA, a line DE in parallel with the line AB and a line EF in parallel with the line BC, thereby to reduce the stepping time OF in comparison with the time OC as is required. With respect to the number of steps defined by the space surrounded by lines ODEF, the points D, E, F are determined on a condition that the speed of pulses is not excessively low or high as will be described hereunder, and there are used the data between the points O and D, the data between the points D and E, and the data between the points B and C for the section between the points E and F. In this case, the time OF can be shortened by drawing the speed of pulses up to that of line AB.
On the other hand, it becomes necessary to adjust the position of pulse motor so as not to lag behind the pulses especially in the time DE, to thereby reduce the vibrations in the accelerating and decelerating directions. Otherwise the speed of pulse motor comes to be decreased before the vibrations are reduced and as the result, the vibrations and sounds are produced. Further even if the line DE is lowered and is drawn up to the starting frequency of the motor, the time OF is prolonged and the vibrations per step are increased. Such phenomena have been the hindrances in practically reducing the accelerating and decelerating vibrations, especially in a region of small number of steps of pulse motor.